CN1940110A - Excellent weldability 490mpa low yield ratio cold shaping steel pipe and its mfg. method - Google Patents

Abstract

The cold molding steel tube of the present invention has a defined chemical composition, and the microcosmic structure of the steel plate comprises 4 to 70 %, by area, polygonal ferrite phase and 0 to 20 %, by area, quasi-polygonal ferrite phase and 0 to 20 %, by area, martensite phase which has an aspect ration (long diameter/short diameter) less than 4.0 and balance bainite phase which has cold molding part having a ratio of plate thickness (t) to outside cold bending diameter (d) less than 10 %. Without SR treatment, a cold molding steel tube having a tension strength more than 490 MPa can be obtained by using the structure.

Description

The 490MPa level low yield ratio cold shaping steel pipe and the manufacture method thereof of welding property excellent

Technical field

The present invention relates to welding property excellent, low yielding ratio and tensile strength is the cold shaping steel pipe and the manufacture method thereof of 490MPa level, particularly can be applicable to the shock resistance excellence CFT (Concrete-Filled Tube) structure buildings the 490MPa level cold shaping steel pipe and be used to make the effective means of this cold shaping steel pipe.

Background technology

In building structure, requiring has excellent shock resistance and resistivity against fire, particularly for the buildings of the described CFT structure of constructing the shock resistance excellence, just need bring into play the cold shaping steel pipe of excellent weldability with high strength, low yielding ratio.

As about satisfying the cold shaping that so the requires characteristic technology of steel pipe, propose to have multiple all the time.For example, open in the flat 6-128641 communique the spy, disclose following technology: the low yielding ratio steel pipe with 600MPa level and 800MPa level is an object, after the hot rolling, the steel plate that air cooling or water-cooled are crossed, t/D (t: thickness of slab, D: scope outer diameter of steel pipes)≤10% is made steel pipe by cold shaping, to be controlled to be the steel plate of yield ratio (YR)≤80-0.8 * t/D, carry out normalizing in 750～850 ℃ temperature range thereafter.

In addition, in No. 252904 communique of patent, disclose following technology: the steel pipe with the low yielding ratio of 590MPa level is an object, make the rolling temperature of finishing for after (Ar3-20 ℃)～(Ar3+120 ℃) is rolled, with the steel plate air cooling to (Ar3-100 ℃)～(Ar3-120 ℃), then quench to normal temperature from this temperature, also carry out temper to the following temperature range of Ac1 point, scope cold shaping at above-mentioned t/D≤10% is a tubulose, anneals 500～600 ℃ temperature range thereafter.

In addition, open in the flat 7-233416 communique the spy and to disclose: the low yielding ratio steel pipe with the 590MPa level is an object, reheat quenches or Q-tempering to the temperature more than the Ac3 point, implement cold shaping and make steel pipe in the scope of described t/D≤10%, thereafter the temperature range normalizing of reheat to 650～750 ℃.

Described each technology, all the cold shaping steel pipe with the low yielding ratio of 590MPa level is an object, still, wherein open in the flat 6-128641 communique the spy, be after cold shaping, to carry out normalizing.In No. 2529042 communique of patent,,, be not preferred from the viewpoint of economy so can cause the productivity in rolling to reduce because be to be as cold as two phase regions in the rolling line sky.

Open in the technology of flat 7-233416 communique described spy, because the element with Cu, Ni etc. serves as to contain by composition in the former material of steel, so the problem that exists former material cost to uprise.In addition, in this technology, though the precipitation strength that brings by interpolation Cu has realized that the intensity of steel pipe improves, but because in heat treatment step, the temperature of exterior side and the inner face side heterogeneity that becomes, the separating out of Cu take place uneven, take place so can fully be contemplated to the deviation of material.

In described arbitrary technology, with the purpose that is reduced to of yield ratio, all need to implement thermal treatment after the cold shaping, this has problems on the point of cost face and productivity.In addition, if use the so-called Delay DQ method of No. 2529042 communique of described patent, then with from the temperature direct quenching (DQ) more than the Ar3 point compare the intensity step-down after the quenching, therefore for its compensation is needed to increase alloying element, consequently make the weldability deterioration.

From as above, as after cold shaping, not implementing heat-treating methods, also propose to have the technology as the spy opens flat 7-109521 communique, in this technology, reheat is to Ac3～1000 ℃ quenching after the hot rolling, continuing the temperature of reheat to 750～850 ℃ quenches, below the Ac1 point, carry out temper, and adopt the steel plate that is controlled at YR (%)≤80-0.8 * t/D, scope at t/D≤10% is made steel pipe by cold shaping, obtain thickness of slab thus: below the 100mm, the YR of tube axial direction is the low yielding ratio 600MPa level steel pipe for building below 80%.

This technology is an object with the low yielding ratio steel pipe of 600MPa level, with be used for after rolling will organize the reheat of the bainiteization welding, the stress that quench, be used for tough property improvement and prevent steel pipe to remove the remollescent tempering of handling etc. be necessary operation, from the residual some problems of the viewpoint of productivity and cost.And in this technology, guarantee this viewpoint from intensity, needing increases alloying element, still has problems on this aspect of weldability.

On the other hand, as the manufacture method of the low yield ratio high tension steel plate of 490MPa level, also propose to have for example special such technology of clear 55-115921 communique of opening.In this technology, be that mode more than 50% is rolling with the accumulation draft below 900 ℃, and more than the Ar3 point, finish rolling, be cooled to below the Ac1 point after, the scope below reheat to 730～850 ℃ is carried out air cooling.

In this technology, (Q ') handles and compares with quenching from two phase region temperature (surpass Ac1 point, be lower than the Ac3 point), the intensity step-down, so carbon equivalent Ceq (JIS) is that weldability is good below 0.40%, its can be applicable to about the thick 32mm of reaching thickness of slab (for example, the steel No.1,2,4～6 of table 1), but,, then need significantly to improve carbon equivalent Ceq (for example No.3 of table 1) if be applied to the thick and heavy steel pipe that cold shaping is used, the consequent is the weldability deterioration, will need preheating.And, because the draft under austenite non-recrystallization zone (about 900～Ar3 point) increases, so can't satisfy the little such prerequisite of the desired sound anisotropy of construction(al)steel.

So, correction (1981) according to new seismic design method, the viscous deformation of steel when building field allows violent earthquake, absorb the energy of earthquake and prevent that heart is included in the high-rise in the such design concept quilt of collapsing of works, therefore as the needed characteristic of steel, just required low yielding ratio.

In the cold shaping steel pipe that is applied to concrete (concrete) filling Steel Cylindrical Column, when applying the cold bend(ing) of the such strictness of t/D:5～10%, be equivalent to about 2.5～5% strain (ε) because pay in t/4 portion, so yielding stress rises, even tensile strength is the steel of 490MPa level, can not guarantee as target yield ratio (yield-point/tensile strength) below 85%.Under such situation, having to implement after the cold shaping with removing of residual stress is the annealing (Stress Relieving:SR processing) of purpose, causes the reduction of the long-term and productivity of expensiveization, duration.

Summary of the invention

The present invention forms in situation so, and its purpose is, a kind of cold shaping steel pipe of low yielding ratio is provided and is used to make the effective means of this cold shaping steel pipe, and it need not implemented SR and handle, and tensile strength is more than 490MPa.

The so-called 490MPa level low yield ratio cold shaping steel pipe of the present invention that can reach described purpose, by following this thickness of slab is that t (mm) steel plate obtains, it has following chemical constitution, contain: the C:0.07～0.18% (meaning of quality %, below identical), Si:0.05～1.0%, Mn:0.7～1.7%, Ti:0.002～0.025%, sol.Al:0.005～0.1%, and N:0.001～0.008%, in addition, also contain from by select the following group that constitutes more than a kind or 2 kinds: (contain 0%) below the Cr:0.6%, Mo:0.5% following (containing 0%) and V:0.08% following (containing 0%), the ratio of Mn content [Mn] and C content [C] satisfies [Mn]/[C]≤15, by the carbon equivalent Ceq value shown in following (1) in 0.34～0.42% scope, and satisfy 1.1～2.6 by the A value shown in following (2) formula, surplus is made up of Fe and unavoidable impurities, and microtexture respectively is made of mutually following: the polygonal ferrite phase of 4～70 area %; The quasi-polygonal ferrite phase of 0～20 area %; With 0～5 area %, aspect ratio (aspect ratio) (major diameter/minor axis) is the island martensite body phase below 4.0; Surplus is the bainite phase, and this cold shaping steel pipe can be that the steel plate of t (mm) obtains from thickness of slab, has t/d and be the cold shaping position below 10% when the outside of described steel pipe cold bend(ing) diameter is d (mm).

Ceq＝[C]+[Si]/24+[Mn]/6+[Ni]/40+[Cr]/5+[Mo]/4+[V]/15 …(1)

Wherein, [C], [Si], [Mn], [Ni], [Cr], [Mo] and [V] represent the content (quality %) of C, Si, Mn, Ni, Cr, Mo and V respectively.

A＝(2.16{Cr}+1)×(3.0{Mo}+1)×(1.75{V}+1)…(2)

Wherein, { Cr}, { Mo} and { V} represents Cr, Mo and the V solid solution capacity (quality %) in steel plate respectively.

In cold shaping steel pipe of the present invention, as required, also containing following element etc. also is effectively, (a) Cu:0.5% following (not containing 0%) and/or Ni:3.0% following (not containing 0%); (b) Nb:0.015% following (not containing 0%); (c) Ca:0.003% following (not containing 0%); (d) rare earth element: (do not contain 0%) below 0.02%, contain composition according to these characteristic of steel pipe is improved.

When making above-mentioned such cold shaping steel pipe, the steel billet that can just have specified chemical composition composition of the present invention is heated to 950～1250 ℃ temperature range, with the austenite non-recrystallization temperature A γ shown in following (3) formula (℃) following accumulation draft finish as (containing 0%) below 60% rolling become steel plate after, quicken to be cooled to below 450 ℃ from the temperature more than the Ar3 transformation temperature with 4～100 ℃/second speed of cooling, then quenching after the temperature range of reheat to 730～830 ℃, is that scope below 10% is carried out cold shaping at aforementioned record t/d then.

Aγ(℃)＝887+467[C]+(6445[Nb]-644√-[Nb])+(732[V]-230√-[V])+890[Ti]+363[Al]-357[Si] …(3)

Wherein, [C], [Nb], [V], [Ti], [Al] and [Si] represent the content (quality %) of C, Nb, V, Ti, Al and Si respectively.

In this manufacture method, preferred additional as inferior condition: the temperature range of (1) reheat to 730～830 ℃ and after quenching, below 500 ℃ described steel plate is being implemented tempering; (2) finish described rolling after, before quickening cooling, carry out " online levelling machine " (in-line leveller) and correct; (3) with steel billet temperature as carrying out cold shaping below 400 ℃.

According to the present invention, by suitably adjusting the chemical constitution of steel plate, and suitably control the volume fraction of each phase in the microtexture, even not implementing SR handles, also can obtain the cold shaping steel pipe of 490MPa level with low yielding ratio, such cold shaping steel pipe can obtain by suitably creating conditions, and resulting steel pipe can be applicable to the buildings of CFT structure.

Embodiment

Present inventors, at thickness of slab is that to have t/d when being d (mm) be cold shaping position below 10% for t (mm), outside cold bend(ing) diameter, tensile strength is in the above steel pipe of 490MPa, in order to reach welding property excellent, and yield ratio below 85%, has been carried out at length research to chemical ingredients composition and microtexture as target value.

Consequently draw drawing a conclusion, for the yield ratio that makes steel pipe reduces, more than the amount of the rising when importantly in advance the yield ratio in steel plate stage being reduced steel pipe and same stretching δ u (reaching the plastic elongation of ultimate load) is increased.

Distinguished then, in order to make low yielding ratio and tensile strength in the steel plate stage and to deposit, make microtexture coexistence become the bainite phase (B) of hard phase and become soft polygonization mutually ferritic phase (the polygonal ferrite phase: α P), the area percentage of this polygonal ferrite phase (α P) is controlled at 40～70%, effective.In addition we know, by making the ferritic phase polygonization that same stretching δ u is increased.

In the steel plate stage (before the cold shaping), when martensite forms island, bringing into play the reduction yield-point, make yield ratio after the cold bend(ing) further be in the effect of low level.The island martensite body, by martensitic phase and austenite mutually (retained austenite phase) blended constitute (Martensite-Austeniteconstitute:M-A phase) mutually, but the retained austenite phase γ R that is present in the island martensite body is phase-changed into processing induction martensite by cold bend(ing), and same stretching δ u is further increased.Also have, when such organizing and implementing cold bend(ing) was become cold shaping steel pipe, the retained austenite in the tissue disappeared mutually, existed as the martensitic phase of phase transformation.

In cold shaping steel pipe of the present invention, from described viewpoint, need suitably control microtexture, the scope of each phase in this tissue (area percentage) limits and the reasons are as follows.

[polygonal ferrite phase α P:40～70 area %]

In order to make yield ratio be in low level, the ferrite (α P) that makes the polygonization that product dislocation density is little in the microtexture after the phase transformation is effectively, in order to reduce yield ratio in advance in the steel plate stage, its area percentage need be controlled at 40～70% scope.If the area percentage of polygonal ferrite phase (α P) surpasses 70%, then in the heavy wall material target strength guarantee difficulty.On the other hand, if the area percentage of polygonal ferrite phase (α P) is lower than 40%, then yield ratio can surpass target value (85%).

In order to satisfy the area percentage condition of this polygonal ferrite phase, need satisfy the composition condition (also comprise and satisfy described formula (1), (2)) of the present invention's regulation, and satisfy described later creating conditions.

[quasi-polygonal ferrite phase α q:0～20 area %]

The quasi-polygonal ferrite phase α q that dislocation desity is high rises intensity, on the other hand, yield ratio is risen, thus few more good more, count about 0～20% with the area percentage.Can be preferably about 0～15%.

The quasi-polygonal ferrite phase is not grown into 6 dihedrals (by JIS G0551 definition), and is not slick and sly, and forms the form of sawtooth.Therefore, quasi-polygonal ferrite can be distinguished by microscope clearly with polygonal ferrite mutually.

[island martensite body phase M-A:0～5 area %]

Martensitic phase in steel plate stage (M) or martensitic-austenitic mixed phase (M-A phase), in order to allow the C in the transformed austenite not, the big part of segregation of alloying element that bainitic transformation does not take place, and become island martensite body phase (M) and retained austenite (γ R) mutually partly.Wherein, martensitic phase (M) acts on tensile strength rising, the reduction of yield ratio effectively.Retained austenite (γ R) because by the processing strain from the outside processing induction phase transformation is occurred, increases so act on same tensile effectively in addition.Therefore, in cold shaping steel pipe, in order further to promote the relative reduction of yield ratio and the increase of same stretching δ u, and make island martensite body phase (also comprise M-A: the martensitic phase M after the phase transformation of retained austenite) generate.The area percentage of island martensite body phase (M-A) can be about 0～5%.If the area percentage of island martensite body phase (M-A) surpasses 5%, then the toughness deterioration.This area percentage can be preferably about 0～4%.

[aspect ratio of island martensite body phase (M-A): below 4.0]

Even the area percentage of island martensite body phase (M-A) is below 5%, if because of its shape aspect ratio (major diameter/minor axis) surpasses 4.0, then same stretching does not increase, and toughness still can deterioration.In addition, because M-A is formed at old austenite grain boundary mutually, so its aspect ratio is controlled at below 4.0, be the little result of range of extension of old austenite material, because the formation of rolling set tissue is also very small, so can reduce the sound anisotropy of seam weldering (seam weld) portion (being equivalent to hold crooked nothing to add the Ministry of worker) of steel pipe.

In cold shaping steel pipe of the present invention, though having thickness of slab is t (mm), t/d was the cold shaping portion below 10% when outside cold bend(ing) diameter was d (mm), but, surpass in 10% such cold working at this t/d, because the yield ratio of tensile deformation side has surpassed 85% after processing, so, need the shaping under heat, the temperature, or anneal of the removal of the stress after being shaped (described SR handles) in order to suppress the rising of yield ratio.For this reason, need described t/d below 10%.This t/d is preferably below 7.5% and is advisable.In the working method that is used for reaching this t/d, be not limited to the shaping of buckling, also can be for example application of roll bending, compression extruding, spinning (spinning) etc.Flexure temperature not only can allow normal temperature in addition, and allows to reach the temperature of the degree (about 400 ℃) of the material of not damaging steel plate of the present invention.Also have, cold shaping steel pipe of the present invention, its cross-sectional shape comprise any of circle, limit shape.In addition, described outside cold bend(ing) diameter d is looked like by the curvature diameter at the position of cold shaping (bending machining), and when the cross-sectional shape of steel pipe was circular, outside cold bend(ing) diameter d was consistent with outer diameter of steel pipes D.

In cold shaping steel pipe of the present invention, ratio (counting 40～70%) for the amount of the ferrite in the control microtexture as above-mentioned (α P) with the area percentage, the ferrite plush copper (nose) that effectively makes transformation curve is to the short period of time side shifting, specifically, the ratio ([Mn]/[C]) that makes Mn content [Mn] and C content [C] exactly makes the two-phase separating purification of the C of two phase regions (α+γ zone) temperature maintenance become easy below 15.In addition, in order to make such effect performance, be effective (about this condition aftermentioned) about 730～830 ℃ as two phase region quenching temperatures.

The hardization of ferritic softening and cementite, be considered to effectively adding segregation element negative concerning ferrite, in the austenite and ferritic coexisting state that in two phase region temperature keep, exists, segregation element negative concerning ferrite is not being spread in the transformed austenite, bainitic transformation is taken place, in the bainitic transformation process, make its alloying element that spues denseization in cementite.

Segregation element as negative for ferrite is conceived to the huge effect of Cr, Mo and V, as its solid solution capacity, the amount of described (2) formula defined is controlled at 1.1～2.6, thereby can makes alloying element two-phase separating purification.Also have, for the amount with described (2) formula regulation is controlled at 1.1～2.6, effectively by steel billet is heated to 950～1250 ℃ temperature range and in rolling end back from the temperature chilling more than the Ar3 transformation temperature, thereby the nitride of realizing described each element is on one side separated out the avoidance of separating out in the temperature province, on one side after Cr, Mo and V become solid solution condition, carry out two phase regions quench (about this condition aftermentioned).

Reducing yield-point and making during same stretching δ u increases, effectively behind ferrite transformation, not have that processing makes it that grain is grown up and polygonization makes ferritic dislocation desity be in low level thus.

In order to reduce the yield ratio of cold shaping steel pipe, and still guarantee toughness, more isotropic martensitic phase is formed, but from this viewpoint, need make described aspect ratio is below 4.0.By making aspect ratio be in low level,, rolling set tails off in addition, so also effective for the anisotropic reduction of sound of the seam weldering portion of steel pipe (being equivalent to hold crooked nothing to add the Ministry of worker) because organizing also.

As the martensitic phase that suppresses the steel plate stage or with the means of the flattening of austenitic mixolimnion, will by the following accumulation draft of the austenite non-recrystallization temperature A γ shown in described (3) formula as 60% below and finish rolling, for the martensitic phase that suppresses to separate out in an old austenite grain and a boundary or effective with the flattening of austenitic mixed phase.In addition, rolling end temp at this moment is from this viewpoint of inhibition of the flattening of old austenite grain, preferably more than austenite non-recrystallization temperature A γ.In addition, in order to control martensitic tissue branch rate in this way, need be with the C in alloying element shown in the present (particularly Cr, Mo, V etc.) the displacement carbon equivalent formula.

In cold shaping steel pipe of the present invention, its microtexture, (surplus) is made of bainite substantially except described, still, the polygonal ferrite α P of the scope of the invention is separated out after, directly quicken cooling in order not make pearlitic transformation and get final product.

So, in cold shaping steel pipe of the present invention, also need weldability good, for this reason, just can suppress formation of martensite or bainiteization in the welded heat affecting zone (HAZ), anti-crackle and HAZ toughness are improved by not adding B.In addition, by the interpolation of Ti, TiN is generated, by making the granular effect performance of the old austenite grain among mother metal and the HAZ, toughness can improve.

The qualification reason of the chemical ingredients composition of cold shaping steel pipe of the present invention then, is described.At first, in the present invention, contain as described: C:0.07～0.18%, Si:0.05～1.0%, Mn:0.7～1.7% (wherein, ratio [Mn]/[C]≤15 of Mn content [Mn] and C content [C]), Ti:0.002～0.025%, sol.Al:0.005～0.1% and N:0.001～0.008%, in addition, also contain by from the following group that constitutes, select more than a kind or 2 kinds: (contain 0%) below the Cr:0.6%, Mo:0.5% following (containing 0%) and V:0.08% following (containing 0%), and need the value of described (1) formula and (2) formula regulation is controlled at suitable scope, the scope of these elements limits and the reasons are as follows.

[C：0.07～0.18％]

Though C is the most cheap in the strength enhancing effective elements, if excessively contain, then weldability significantly reduces, thus its content on be limited to 0.18%.Yet, if C content is lower than 0.07%, undercapacity takes place, for it is remedied, just need the interpolation of alloying element, but, then cause the increase of yield ratio if carry out the interpolation of these alloying elements too much, be not preferred therefore.For increase that suppresses this yield ratio and the intensity (more than tensile strength 490MPa) of guaranteeing target, need at least C is contained more than 0.07%.Also have, from strength of parent and welded H AZ toughness and the viewpoint of depositing, the preferred lower limit of C content is 0.08%, and preferred upper limit is 0.16%.

[Si：0.05～1.0％]

Contain more than 0.05% for deoxidation need make Si, but, weldability and HAZ toughness are reduced if make it excessively to contain above 1.0%.Set out thus, Si content need for: 0.05～1.0%.Also have, the preferred lower limit of Si content is 0.10%, and preferred upper limit is 0.9%.

[Mn:0.7～1.7% (wherein, ratio [Mn]/[C]≤15 of Mn content [Mn] and C content [C])]

The Mn conduct improves intensity simultaneously and the flexible element is effective.In order to make such effect performance, Mn is contained more than 0.7%.Yet if Mn is excessively contained, weldability and the remarkable deterioration of HAZ toughness, so be limited to 1.7% on it.Also have, the preferred lower limit of Mn content is 1.0%, and preferred upper limit is 1.6%.

In addition, Mn content is by adjusting to suitable scope with the relation of C content.Ratio [Mn]/[C] of Mn content [Mn] and C content [C], become on composition the factor of degree of outstanding (plush copper nose) of the ferritic phase varied curve of control continuous cooling transformation curve (CCT curve) and isothermal phase change curve (TTT curve), surpass 15 as if described than [Mn]/[C], then the ferrite plush copper is moved back to long-time rear flank, therefore (hold-time of α+γ) is elongated, is restricted and poor efficiency on producing to be used for forming two phase constitutions of equilibrium state by two phase region thermal treatments (Q ').For this reason, described need be than [Mn]/[C] for below 15.

[Ti：0.002～0.025％]

Ti exists as trickle TiN in steel when slab (slab) heats, and has the effect of thickization that prevents to heat the austenite grain.The composite effect that utilizes the rolling and trickle TiN in γ non-recrystallization temperature A γ territory rolling, that follow, suitable austenite (γ) recrystallization temperature zone to generate can be guaranteed good toughness and ultrasonic wave sound anisotropy.During the Q ' of Ti after direct quenching handles in addition, also from the reverse transformation austenite, be ferrite transformation nuclear with TiN, make the promotion of separating out of polygonal ferrite, yield ratio is reduced, the increase of same stretching δ u is effective.In order to make such effect performance, Ti content need be for more than 0.002%.Yet, also be saturated because make Ti excessively contain its effect, so be limited to 0.025% on it.Also have, the preferred lower limit of Ti content is 0.008%, and preferred upper limit is 0.015%.

[sol.Al：0.005～0.1％]

Contain 0.005% for deoxidation needs to make sol.Al (soluble aluminum) at least, but if make it excessively to contain, then non-metallic inclusion increases and the toughness reduction, so it need be for below 0.1%.Also have, the preferred lower limit of sol.Al content is 0.01%, and preferred upper limit is 0.06%.

[N：0.001～0.008％]

N and Ti reaction generates TiN, is the effective elements of austenitic thickization when preventing to heat.In order to make such effect performance, need at least to make it to contain more than 0.001%, but if making it excessive contains the then toughness deterioration of fusion splice portion, so it need be below 0.008%.Also have, N content preferred lower limit is 0.002%, and preferred upper limit is 0.006%.

[below Cr:0.6%, (contains 0%), (contains 0%) below the Mo:0.5% and (contain 0%) below the V:0.08% the group that is constituted and select more than a kind or 2 kinds, and solid solution capacity satisfies the amount of described (2) formula]

Cr, Mo and V are the elements that intensity is improved, and when still separating out as compound, rise owing to precipitation strength makes yield ratio, can make the toughness deterioration on the other hand.Guarantee high strength and high tenacity in order to make yield ratio remain on the state of low level, effectively at cementite positive segregation is taken place, negative segregation is taken place at ferrite with solid solution condition.Set out thus, need the content of Cr, Mo and V to be respectively below 0.6%, (all contain 0%) below 0.5%, below 0.08%, the A value by described (2) formula regulation is controlled at its solid solution capacity in 1.1～2.6 the scope.If this composition amount of element and A value surpass the upper limit, then can damage weldability.In addition, if the A value is lower than 1.1, then the yield ratio behind the steel tube forming can not satisfy target value.Also have, each element is preferably that Cr:0.3% is following, Mo:0.3% is following, is advisable below the V:0.06%.In addition, the preferable range of A value is about 1.05～2.0.

[Ceq：0.34～0.42％]

The carbon equivalent Ceq that described (1) formula is represented be the expression HAZ indurative index (for example, JIS G 3106), in order to reduce crack sensitivity, make the crack in the y-shaped weld crack test prevent that preheating temperature from being below 25 ℃, need be with the Ceq value as below 0.42%.On the other hand, more than 490MPa, the Ceq value need be for more than 0.34% in order to ensure tensile strength.The preferred lower limit of Ceq value is 0.36%, and preferred upper limit is 0.40%.Also have, in described (1) formula, except as C, the Si of basal component, Mn, Cr, Mo, the V etc., the composition (Ni) that also comprises as required to be contained as the project in the formula, but, to consider its content when containing these compositions and calculate, can consider its content when not comprising and calculate as the value of (1) formula.

In cold shaping steel pipe of the present invention, beyond the described composition, form by Fe and unavoidable impurities, but, (for example also can comprise the trace ingredients (permission composition) of sneaking into inevitably in the melting, P, S, O, B≤0.0005% etc.), such plate slab also is contained in scope of the present invention.In addition, in cold shaping steel pipe of the present invention, as required, it also is effective containing further that following one-tenth grades: (a) Cu:0.5% following (not containing 0%) and/or Ni:3.0% following (not containing 0%); (b) Nb:0.015% (not containing 0%); (c) Ca:0.003% following (not containing 0%); (d) rare earth element: (do not contain 0%) below 0.02%, the scope when containing these compositions limits and the reasons are as follows.

[Cu:0.5% following (not containing 0%) and/or Ni:3.0% following (not containing 0%)]

Because these element costlinesses, and yield ratio is risen, so its interpolation is preferably avoided as much as possible.But, because have the effect of the intensity reduction that in thick steel sheet, suppresses the thickness of slab central part, so trace adds sometimes.When adding these elements, need make Cu is that the upper limit, Ni are that the upper limit contains with 3.0% with 0.5%.Cu content more preferably on be limited to 0.3%, Ni more preferably on be limited to 1.5%.

[Nb:0.015% (not containing 0%)]

Nb is known to be the element that intensity and toughness are improved, but is quickening after the hot rolling under the refrigerative situation, and in the steel that contains the Nb that improves element as hardenability, the bainite amount of second phase constitution increases, and soft ferrite is difficult to generate.Consequently, yield ratio rises.Set out thus, when containing Nb, preferably to about 0.015%.Nb content more preferably on be limited to about 0.010%.

[Ca:0.005% following (not containing 0%)]

Ca has the balling effect of non-metallic inclusion, helps anisotropic reduction, but if contain above 0.005%, then because the increase toughness of inclusion can deterioration.Therefore, Ca is contained sometimes, be preferably below 0.005%.The preferred lower limit of Ca content is 0.0005%, is limited to 0.003% on more preferably.

[rare earth element: (do not contain 0%) below 0.02%]

Rare earth element (following simple record is REM), be under TiN coexistence, to suppress unusual growth of austenite and element that the toughness of HAZ is improved as its oxysulfide (oxysulfide), but excessively contain if surpass 0.02%, then destroy the purity of steel, subsurface defect is taken place.In order to make from the performance of the effect of REM, preferably make it to contain more than 0.002%, be limited to 0.01% on more preferably.Also have, so-called REM all can use so long as belong to scandium (Sc), yttrium (Y) and group of the lanthanides (lanthanoid) rare earth element of periodictable the 3rd family.

In order to make cold shaping steel pipe of the present invention, basically adopt the steel billet of the slab of free Continuous casting process and ingot casting method made, operation through the operation of heating-hot rolling-cooling-thermal treatment etc. or the controlled chilling after the hot rolling (also comprise and quicken cooling and direct quenching) etc., can produce thus and have the steel pipe that described such chemical ingredients is formed and organized, therefore this manufacture method is not particularly limited (experiment No.42～46 of aftermentioned embodiment), but preferably follows the inventive method and make.Next each prerequisite by manufacture method regulation of the present invention is described.

[Heating temperature of steel billet: 950～1250 ℃]

If the Heating temperature of steel billet is as the temperature that surpasses 1250 ℃, then the austenite grain of steel billet causes rapid grain growth, and microstructure after phase transformation becomes thick bainite structure, and the toughness of steel plate becomes significant low level.On the other hand; if Heating temperature is lower than 950 ℃; the accumulation draft that then is lower than under (γ-50 ℃ of γ non-recrystallization temperature A) becomes big, causes the excessive grain refined of old austenite grain, and yield-point YP, 0.2% ultimate stress σ 0.2 and yield ratio YR will rise significantly.Set out thus, the Heating temperature of steel billet need be 950～1250 ℃ scope.This Heating temperature can be preferably more than 1000 ℃, below 1150 ℃.

[the accumulation draft below γ non-recrystallization temperature A γ is below 60%]

As previously mentioned, for the martensitic phase that suppresses the steel plate stage or with the flattening of austenite mixed phase mutually, the accumulation draft below γ non-recrystallization temperature A γ need be for below 60%.If should surpass 60% by long-pending draft, then cause the excessive grain refined of old austenite grain in addition, yield ratio will rise.Also have, so-called described " draft " is the thickness of the steel plate of rolling front and back during respectively as t1 (mm) and t2 (mm), by (t1-2)/(%) is represented in t1} * 100.

[after the rolling end, being cooled to below 450 ℃ from acceleration more than the Ar3 transformation temperature] with 4～100 ℃/second speed of cooling

Realize that the solid solution of the homogeneous dispersion of the C in the microtexture of steel plate and Cr, Mo, V also guarantees intensity, with this end in view just need be cooled to below 450 ℃ from acceleration more than the Ar3 transformation temperature after rolling.Cooling beginning temperature can become lower than Ar3 transformation temperature, cooling stops temperature and becomes than 450 ℃ high, if speed of cooling is lower than 4 ℃/second, then phase transformation strengthening is insufficient (promptly, second of two-phase structure is difficult to become bainite mutually), and the whole solid solutions that can't reach Cr, Mo and V.About the upper limit of at this moment speed of cooling, from the cooling of cooling medium can this viewpoint of boundary, need be with it as below 100 ℃/second.Also have, so-called Ar3 transformation temperature of the present invention adopts the value of calculating according to following (4) formula.

Ar3 transformation temperature=910-310[C]-80[Mn]-20[Cu]-15[Cr]-55[Ni]-80[Mo]+0.35 (t-8) ... (4)

Wherein, t: thickness of slab

[after the temperature range of reheat to 730～830 ℃, quenching]

Remain on the two phase regions (temperature of α+γ) by will speed up the refrigerative steel plate, temporary transient dispersive C, be separated to quasi-polygonal ferrite and the reverse transformation austenite that when quickening cooling, is generated by two-phase, the negative segregation (concentration than mean concns (addition) is low) of the C in the quasi-polygonal ferrite, austenitic positive segregation (than the concentration height of mean concns (addition)) are taken place.In addition, by quickening cooling, even in each element of Cr, the Mo of temporary transient solid solution and V, under this two phase region keeps, also can make negative segregation, take place, can solve the reduction of yield ratio and high-intensityly guarantee this opposite problem to austenitic positive segregation to quasi-polygonal ferrite.When this two phase region keeps down temperature to be lower than 730 ℃ and when surpassing 830 ℃, because the reverse transformation Ovshinsky scale of construction, quasi-polygonal ferrite amount are very few, so the yield ratio in steel plate stage uprises, the yield ratio behind the cold shaping steel pipe can not satisfy the target yield ratio respectively.Quenching after why remaining on two phase region temperature in addition, is in order by quenching from the reverse transformation austenite bainite structure of principal phase to be separated out mutually with the island martensite body again.

[thickness of slab is as t (mm), and outside cold bend(ing) diameter is during as d (mm), is that scope below 10% is carried out cold shaping at t/d]

In cold shaping steel pipe of the present invention, in order to allow the yield ratio of tensile deformation side become below 85% after the processing, be cold shaping part below 10% and have t/d, still, in order to be shaped this position, be that scope below 10% is carried out cold shaping at t/d.

In manufacture method of the present invention, as required and preferred additional as inferior condition: the temperature range of (1) reheat to 730～830 ℃, after quenching from this scope, below 500 ℃ described steel plate is being implemented tempering; (2) finish described rolling after, before quickening cooling, carry out online levelling machine and correct; (3) steel billet temperature is made as carries out cold shaping below 400 ℃, stipulate the reasons are as follows of these prerequisites.

[temperature range of reheat to 730～830 ℃, do quenching from this scope after, below 500 ℃ described steel plate is being implemented tempering]

In order to eliminate the residual stress of the steel plate that two phase regions quenched, optionally in that to implement tempering below 500 ℃ also effective.If tempering temperature at this moment surpasses 500 ℃, then the C in the bainite structure of as-quenched condition generation spreads aggegation and perlite is generated, so intensity can reduce.Set out thus, tempering temperature should be preferably below 480 ℃ below 500 ℃.

[finish described rolling after, before quickening cooling, carry out online levelling machine and correct]

After the rolling end, smooth bad even the front and back end of the steel plate after rolling sometimes can produce, make Flatness good by the hot straightening before the direct quenching, thereby can carry out homogeneous cooling the end, front and back, mechanical properties is stable, and productivity improves.Set out thus, effectively before rolling end back direct quenching, carry out online levelling machine and correct.

[be made as steel billet temperature carry out cold shaping below 400 ℃]

Flexure temperature (forming temperature) is as above-mentioned, not only can allow normal temperature, and allow to reach the temperature of the degree (about 400 ℃) of the material of not damaging steel plate of the present invention, but the shaping hindering factor of retarded elasticity (springback) when alleviating cold shaping etc., and microtexture is changed, optionally be shaped below 400 ℃ (warm working) that can allow dislocation desity reduce is also effective.If at this moment forming temperature surpasses 400 ℃, then the part of the bainite of C diffusion and principal phase begins to be varied to perlite, thereby will cause intensity to reduce.The preferred temperature of this formation temperature is below 300 ℃.

Below, be described more specifically the present invention by embodiment, but the present invention is not limited by following embodiment certainly, certainly the scope of aim described later is changed enforcement before can meeting, and these all are included in the scope of technology of the present invention.

[embodiment]

According to the steel that the chemical ingredients shown in the common following table 1 of melting method melting, 2 is formed, carry out the every processing (Class1～3) shown in following, make steel plate.Also have, in table 1,2, by the value of the carbon equivalent Ceq of described (1) formula regulation, also value and the γ non-recrystallization temperature of expression [Mn]/[C].

[treatment step]

Class1: after carrying out common heating, hot rolling, carry out direct quenching (DQ), after thermal treatment keeps, quench (Q ') with two phase region temperature (more than the Ac1 point, being lower than the Ac3 point) thereafter or heating is cooled to below 500 ℃.

Type 2: after the rolling end, slowly cooling to of air cooling degree is lower than after the Ar3 point, quickens cooling or direct quenching (DQ ') from two phase region temperature (surpass Ar1 point, be lower than the Ar3 point).

Type 3: after the hot rolling, after quickening cooling and remaining on two phase region temperature, quicken cooling or direct quenching (DQ ') again.

Thereafter, wherein a part except the tempering (T) that is not lower than the temperature that Ac1 orders, has been implemented tempering.Creating conditions at this moment is with expression in following table 3～5 such as the value of described (2) formula and Ar3 transformation temperature.

[table 1]

Steel grade	Chemical ingredients is formed (quality %)															Ceq (％)	[Mn] /[C]	γ non-recrystallization temperature (℃)
																			C	Si	Mn	P	S	sol.Al	Ti	Cr	Mo	V	Cu	Ni	Nb	N	Other
	A	0.17	0.45	1.40	0.015	0.004	0.030	-	-	-	0.060	-	-	-	0.0040																			-	0.426	8.2	804
B																0.14	0.35	1.25	0.007	0.002	0.035	0.013	-	-	-	-	-	0.008	0.0040	-	0.363	8.9	846
	C	0.14	0.15	1.25	0.007	0.002	0.035	0.013	0.10	-	0.040	-	-	-	0.0040																			-	0.377	8.9	906
D																0.14	0.15	1.25	0.007	0.002	0.035	0.013	-	-	0.040	-	-	-	0.0040	-	0.382	8.9	906
	E	0.14	0.15	1.25	0.007	0.002	0.035	0.013	0.10	-	-	-	-	-	0.0040																			-	0.387	8.9	923
F																0.10	0.15	1.50	0.007	0.002	0.035	0.013	0.10	-	-	-	-	-	0.0040	-	0.389	15.0	904
	G	0.10	0.15	1.10	0.007	0.002	0.035	0.013	0.49	-	0.040	-	-	-	0.0040																			-	0.410	11.0	898
H																0.14	0.35	1.25	0.007	0.002	0.035	0.013	0.02	-	0.010	-	-	-	0.0040	-	0.371	8.9	836
	I	0.18	0.05	1.05	0.007	0.002	0.035	0.013	0.10	-	-	-	0.15	0.008	0.0040																			-	0.393	5.8	971
J																0.18	0.05	1.05	0.007	0.002	0.035	0.013	0.10	-	-	-	0.15	0.008	0.0040	-	0.393	5.8	960
	K	0.07	0.15	1.10	0.007	0.002	0.035	0.013	0.20	-	0.010	-	-	0.008	0.0040																			-	0.350	15.0	869
L																0.20	0.15	1.10	0.007	0.002	0.035	0.013	0.10	-	0.040	-	-	-	0.0040	-	0.412	6.8	934
	M	0.05	0.15	1.80	0.007	0.002	0.035	0.013	0.10	-	0.040	-	-	-	0.0040																			-	0.379	36.0	864
N																0.115	0.15	1.70	0.007	0.002	0.035	0.013	0.09	-	0.040	-	-	-	0.0040	-	0.425	14.8	895
	O	0.16	0.15	0.70	0.007	0.002	0.035	0.013	0.60	-	0.080	-	-	-	0.0040																			-	0.409	4.4	926
P																0.05	0.15	0.50	0.007	0.002	0.035	0.013	0.10	-	0.040	-	-	-	0.0040	-	0.162	10.0	864
	Q	0.14	0.15	1.25	0.007	0.002	0.10	0.013	0.10	-	0.040	-	-	-	0.0040																			-	0.377	8.9	930
R																0.14	0.15	1.25	0.007	0.002	0.005	0.013	0.10	-	0.040	-	-	-	0.0040	-	0.377	8.9	896

[table 2]

Steel grade	Chemical ingredients is formed (quality %)															Ceq (％)	[Mn]/ [C]	γ non-recrystallization temperature (℃)
																			C	Si	Mn	P	S	sol.Al	Ti	Cr	Mo	V	Cu	Ni	Nb	N	Other
	S	0.14	0.15	1.25	0.007	0.002	0.035	0.025	0.10	-	-	-	-	-	0.0040																			-	0.377	8.9	917
T																0.14	0.15	1.25	0.007	0.002	0.035	0.040	0.10	-	-	-	-	-	0.0040	-	0.377	8.9	930
	U	0.10	0.15	1.05	0.007	0.002	0.035	0.013	-	-	-	-	-	-	0.0040																			-	0.406	10.5	904
V																0.10	0.15	1.05	0.007	0.002	0.035	0.013	-	-	-	-	-	-	0.0040	-	0.456	10.5	904
	W	0.14	0.15	1.25	0.007	0.002	0.035	0.013	0.10	-	0.08	-	-	-	0.0040																			-	0.374	8.9	917
X																0.14	0.15	1.50	0.007	0.002	0.035	0.013	0.10	-	0.040	-	-	-	0.0040	-	0.419	10.7	906
	Y	0.12	0.15	1.15	0.007	0.002	0.035	0.013	0.10	-	0.040	-	-	-	0.0040																			-	0.340	9.6	897
Z																0.12	1.00	1.25	0.007	0.002	0.035	0.013	0.10	-	0.040	-	-	-	0.0040	-	0.393	10.4	594
	A1	0.12	1.50	1.25	0.007	0.002	0.035	0.013	0.10	-	0.040	-	-	-	0.0040																			-	0.414	10.4	415
B1																0.14	0.15	1.25	0.007	0.002	0.035	0.013	-	0.10	0.040	0.5	0.5	-	0.0040	-	0.395	8.9	906
	C1	0.12	0.15	1.25	0.007	0.002	0.035	0.013	-	0.10	0.040	-	3.0	-	0.0040																			-	0.437	10.4	897
D1																0.14	0.15	1.25	0.007	0.002	0.035	0.013	-	0.10	0.040	1.0	1.0	-	0.0040	-	0.407	8.9	906
	E1	0.12	0.15	1.25	0.007	0.002	0.035	0.013	-	0.10	0.040	1.0	3.5	-	0.0040																			-	0.450	10.4	897
F1																0.14	0.15	1.25	0.007	0.002	0.035	0.013	-	0.10	0.040	-	-	0.015	0.0040	-	0.382	10.4	924
	G1	0.14	0.15	1.25	0.007	0.002	0.035	0.013	-	0.10	0.040	-	-	0.005	0.0040																			-	0.382	10.4	988
H1																0.14	0.15	1.25	0.007	0.003	0.035	0.013	0.10	-	0.040	-	-	-	0.0040	Ca：0.0030	0.377	10.4	906
	I1	0.14	0.15	1.25	0.007	0.002	0.035	0.013	0.10	-	0.040	-	-	-	0.0040																			REM：0.020	0.377	10.4	906
J1																0.14	0.15	1.25	0.007	0.002	0.035	0.013	0.10	-	0.40	-	-	-	0.0040	Ca：0.0070， REM：0.025	0.376	10.4	906

[table 3]

Test No.	Steel grade	Make type	Heating temperature (℃)	The accumulation draft (%) in γ non-recrystallization territory	Rolling finish temperature (℃)	Thickness of slab (mm)	Acceleration cooling after rolling			Heat-treat condition (℃)		The A value	The Ar3 transformation temperature (℃)
														The beginning temperature (℃)	Speed of cooling (℃/s)	Stop temperature (℃)	Q’	T
							1	A	Photographic developer	1100	60								850	70	-	Air cooling	-	-	-	1.02	767
2	B	1	1100	60	850	70						820	7	450	-	500	1.00	788
							3	B	1	1100	60								850	70	820	7	450	770	500	1.00	788
4	C	1	1100	60	850	70						820	7	25	770	500	1.24	787
							5	D	1	1100	60								850	70	820	7	25	770	500	1.32	787
6	E	1	1100	60	850	70						820	7	25	770	500	1.40	780
							7	E	1	1100	60								850	70	820	7	25	770	500	1.40	783
8	F	1	1100	60	850	70						820	7	25	770	500	1.40	775
							9	G	1	1100	60								850	70	820	7	25	770	500	2.60	799
10	H	1	1100	60	850	70						820	7	25	770	500	1.11	787
							11	I	1	1100	60								850	70	820	7	25	770	500	1.11	778
12	J	1	1100	60	850	70						820	7	25	770	500	1.11	778
							13	K	1	1100	65								850	70	820	7	25	770	500	2.33	803
14	L	1	1100	60	850	70						820	7	25	770	500	1.24	780
							15	M	1	1100	70								850	70	820	7	25	770	500	1.24	771
16	N	1	1100	60	850	70						820	7	25	770	500	1.13	759
							17	O	1	1100	60								850	70	820	7	25	770	500	2.33	817
18	P	1	1100	70	850	40						820	17	25	770	500	1.22	864
							19	Q	1	1100	60								850	70	820	7	25	770	500	1.24	787
20	R	1	1100	60	850	70						820	7	25	770	500	1.24	787
							21	S	1	1100	60								850	70	820	7	25	770	500	1.24	787
22	T	1	1100	60	850	70						820	7	25	770	500	1.24	787
							23	U	1	1100	60								850	70	820	7	25	770	500	2.50	777
24	V	1	1100	60	850	70						820	7	25	770	500	3.10	761
							25	W	1	1100	60								850	70	820	7	25	770	500	1.22	767

[table 4]

Test No.	Steel grade	Make type	Heating temperature (℃)	The accumulation draft (%) in γ non-recrystallization territory	Rolling finish temperature (℃)	Thickness of slab (mm)	Acceleration cooling after rolling			The maintenance method	The cooling second time after rolling			Heat-treat condition (℃)		The A value	The Ar3 transformation temperature (℃)
																		The beginning temperature (℃)	Speed of cooling (℃/s)	Stop temperature (℃)	The beginning temperature (℃)	Speed of cooling (℃/s)	Stop temperature (℃)	Q’	T
							26	X	1		1100	60	850	70	820											7	25	-	-	-	-	770	-	1.24	767
27	Y	1	1100	60	850	70				820						7	25	-	-	-	-	770	-	1.24	801
							28	Z	1		1100	60	850	70	820											7	25	-	-	-	-	730	-	1.24	793
29	A1	1	1100	60	850	70				820						7	25	-	-	-	-	730	-	1.24	793
							30	B1	1		1100	60	850	70	820											7	25	-	-	-	-	770	-	1.32	743
31	C1	1	1100	60	850	70				820						7	25	-	-	-	-	770	-	1.32	622
							32	D1	1		1100	60	850	70	820											7	25	-	-	-	-	770	-	1.32	705
33	E1	1	1100	60	850	70				820						7	25	-	-	-	-	770	-	1.32	574
							34	F1	1		1100	60	850	100	820											7	25	-	-	-	-	770	-	1.32	791
35	G1	1	1150	60	850	100				820						7	25	-	-	-	-	770	-	1.24	791
							36	H1	1		1100	60	850	70	820											7	25	-	-	-	-	770	-	1.24	787
37	I1	1	1100	60	850	70				820						7	25	-	-	-	-	770	-	1.24	787
							38	J1	1		1100	60	850	70	820											7	25	-	-	-	-	770	-	1.24	787
39	C	1	1100	60	850	70				820						7	25	-	-	-	-	770	-	1.28	787
							40	C	1		1100	60	850	70	820											7	450	-	-	-	-	770	-	1.24	787
41	C	1	1100	60	850	70				820						7	450	-	-	-	-	770	500	1.22	787
							42	C	2		1100	60	850	70	820											0.3	750	-	750	7	25	770	-	1.29	787
43	C	2	1100	60	850	70				820						0.3	750	-	750	7	25	770	500	1.22	776
							44	C	3		1100	60	850	70	820											7	720	60 seconds (air cooling)	708	7	25	770	-	1.29	787
45	C	3	1100	60	850	70				820						7	720	770 ℃ 60 minutes (online maintenance stove)	770	7	300	770	-	1.26	787
							46	C	3		1100	60	850	70	820											0.3	720	770 ℃ 60 minutes (online maintenance stove)	770	7	25	770	500	1.25	787
47	C	1	1100	60	850	70				820						7	25	-	-	-	-	770	-	1.24	787
							48	C	1		1100	60	850	70	820											7	25	-	-	-	-	770	-	1.24	787
49	C	1	1100	60	850	40				820						17	25	-	-	-	-	770	-	1.24	776
							50	C	1		1100	60	850	70	820											7	25	-	-	-	-	770	-	1.24	787

[table 5]

Test No.	Steel grade	Make type	Heating temperature (℃)	The accumulation draft (%) in γ non-recrystallization territory	Rolling finish temperature (℃)	Thickness of slab (mm)	Acceleration cooling after rolling			Heat-treat condition (℃)		The A value	The Ar3 transformation temperature (℃)
														The beginning temperature (℃)	Speed of cooling (℃/s)	Stop temperature (℃)	Q’	T
							51	C	1	1300	60								850	70	820	7	25	770	-	1.24	787
52	C	1	1250	60	850	70						820	7	25	-	-	1.24	787
							53	C	1	950	60								850	70	820	7	25	-	-	1.24	787
54	C	1	900	100	850	70						820	7	25	-	-	1.24	787
							55	C	1	1100	80								850	70	820	7	25	770	-	1.24	787
56	C	1	1100	0	850	70						820	7	25	-	-	1.24	787
							57	C	1	1100	60								850	70	820	7	25	-	-	1.24	787
58	C	1	1100	60	850	70						760	7	25	-	-	1.24	787
							59	C	1	1100	60								850	70	820	7	450	770	-	1.24	787
60	C	1	1150	60	850	70						820	7	580	-	-	1.24	787
							61	C	1	1100	60								850	70	820	1.5	450	-	-	1.24	787
62	C	1	1100	60	850	20						820	100	25	740	-	1.23	770
							63	C	1	1100	60								850	70	820	7	25	850	-	1.29	787
64	C	1	1100	60	850	70						820	7	25	830	-	1.27	787
							65	C	1	1100	60								850	70	820	7	450	730	-	1.27	787
66	C	1	1100	60	850	70						820	7	450	700	-	1.22	787
							67	C	1	1100	60								850	70	820	0.5	750	770	500	1.24	787
68	C	1	1100	60	850	70						820	0.5	750	770	600	1.24	787
							69	C	1	1100	60								850	70	806	7	720	770	-	1.24	787
70	C	1	1100	60	850	70						820	7	720	770	-	1.24	787
							71	C	1	1100	60								850	70	820	0.5	720	770	-	1.24	787

For resulting each steel plate, t/d is changed, carry out cold-press moulding, make steel pipe.The characteristic (yield-point YP, tensile strength TS, same stretching δ u) of the machinery of mensuration steel plate and the kind of microtexture, and the tubular axis of measuring steel pipe is to solid solution capacity and the microtexture of the characteristic (yield-point, tensile strength TS, yield ratio YR and toughness) of the machinery of (L direction) and Cr, Mo, V, with following benchmark evaluation material.

[solid solution capacity of Cr, Mo, V]

In the solid solution capacity of Cr, the Mo of steel pipe and V, calculate as each amount of element of the addition of each element-separate out as precipitate.To as precipitate and Cr, the Mo that separates out, the amount of element of V, with the surperficial parallel cross section of the outside t/4 portion of steel pipe in, measure by electrowinning residue method and to separate out amount of element.

[material judgement criteria]

As the material judgement criteria, with the following target that is set at: the tubular axis of steel pipe to tensile strength TS:490MPa more than; Below the yield ratio YR:85%; Fracture transition temperature (vTrs): below 20 ℃.

The evaluation method of the characteristic (steel plate and steel pipe) of machinery, the toughness evaluation method of steel pipe and microtexture measuring method such as following.

[evaluation method of the characteristic of machinery]

From the t/4 portion (t is a thickness of slab) of steel plate along L direction (rolling direction) and with the tubular axis parallel direction (the main rolling direction that is equivalent to steel plate) of the outside t/4 portion of steel pipe, take No. 22014 test films of JIS Z, main points with JIS Z 2201 are carried out tension test, measure the characteristic (yield-point YP, tensile strength TS, same stretching δ u) of the machinery of steel plate, the mechanical characteristics of steel pipe (yield-point YP, tensile strength TS, yield ratio (Qu Fudian/tensile strength * 100%): YR).

[toughness evaluation method]

From the outside t/4 portion and the tubular axis parallel direction of steel pipe, take No. 22024 test films of JIS Z, carry out pendulum impact test according to JIS Z 2202, measure fracture transition temperature (vTrs).

[microtexture measuring method]

In the steel plate stage, microtexture with the t/4 portion of the main rolling direction of observation by light microscope steel plate, to the retained austenite γ R that exists, carrying out electrolytic polishing is the X-ray diffraction of the steel plate t/4 portion of 50～100 μ m, confirms the existence of retained austenite γ R according to the peak strength ratio of α-Fe (200) face and γ-Fe (200) face.To with the t/4 portion of the main rolling direction of the outside t/4 portion of the tubular axis parallel direction (the main rolling direction that is equivalent to steel plate) of steel pipe and steel plate, to the etch of nitric acid ethanol the photo of microtexture carry out image analysis, measure ferritic form (polygonal ferrite α P, quasi-polygonal ferrite α q), their area percentage, the area percentage of bainite (B), the area percentage of perlite (P) etc.Island martensite body phase (M-A) to LePera reagent image analysis being done in the description of 1/4 corrosive microtexture of rolling direction plate thickness surface, is measured area percentage and aspect ratio.

To satisfying the steel pipe of described material standard, estimate weldability (anti-weld crack and HAZ toughness) according to following method.

[anti-weld crack]

Follow the y-shaped weld crack test method(s) that is defined as JIS Z 3158, carry out the carbonic acid gas welding, measure root crack (root crack) and prevent preheating temperature with input heat: 1.7KJ/mm.Be qualified below 25 ℃.

[HAZ toughness]

Import the seam weldering (X groove) of the two-sided submerged arc welding (SAW) of heat 7KJ/mm, take pendulum impact test sheet (No. 22044, JIS Z) from outside t/4 portion and the tubular axis direction that meets at right angles, the average shock absorption of trying to achieve 0 ℃ can vE0 (3 times test mean values).Average vE0 is that 47J is above for qualified.

The solderability test result shows in following table 6～8 with mechanical characteristics (steel plate and steel pipe) and microtexture etc., still, can carry out following investigation by these results.At first, experiment No.1 is the controlled rolling material that V adds steel separately, because Ceq surpasses the scope of the present invention's regulation, so anti-welding prevents preheating temperature up to 50 ℃, HAZ toughness is also at low level.

Experiment No.2 is that the acceleration cooling that Nb adds steel separately stops material for 450 ℃, because generate in microtexture polygonal ferrite is not arranged, so the discontented foot-eye value of yield ratio YR below 85% after the cold bend(ing).

Experiment No.3 is after 450 ℃ of the acceleration coolings that Nb adds steel separately stop, two phase region temperature quench (Q ') have been carried out, because the area percentage specialized range of the present invention of polygonal ferrite phase is few, so the discontented foot-eye value of the yield ratio YR after the cold bend(ing) is below 85%.

Though the value (A value) of experiment No.14 described (2) formula is in the scope of the present invention's regulation, C content is more than the scope of the present invention's regulation, so the toughness of mother metal and HAZ is at low level.

Its Mn content of experiment No.15 is more than the scope of the present invention's regulation, and the discontented foot-eye value of the yield ratio YR after the cold bend(ing) is below 85%.

Experiment its C content of No.18 and Mn content lack than the scope of the present invention's regulation, more than the 490MPa of the discontented foot-eye value of the anti-line strength TS after the cold bend(ing).

Its Ti content of experiment No.22 is more than the scope of the present invention's regulation, and the discontented foot-eye value of the yield ratio YR after the cold bend(ing) is below 85%.

Its Mo content of experiment No.24 is more than the scope of the present invention's regulation, more than the 47J of the discontented foot-eye value of HAZ toughness.

Its Si content of experiment No.29 is more than the scope of the present invention's regulation, and the island martensite body of steel pipe divides rate more than the scope of the present invention's regulation, and the discontented foot-eye value of the yield ratio YR after the cold bend(ing) is below 85%.

Experiment No.32 its Cu content is more than the scope of the present invention's regulation, and anti-welding prevents that preheating temperature is discontented with below 25 ℃ of foot-eye.Not satisfying fracture transition temperature vTrs in addition is below-20 ℃ and HAZ toughness is the above target value of 47J.

Its Nb content of experiment No.35 is more than the scope of the present invention's regulation, and the discontented foot-eye value of the yield ratio YR after the cold bend(ing) is below 85%.

The content of experiment its Ca of No.38 and REM is more than the scope of the present invention's regulation, and the fracture transition temperature vTrs after the cold bend(ing) does not satisfy below-20 ℃.

Its Heating temperature of experiment No.51 is 1300 ℃, and the fracture transition temperature vTrs after the cold bend(ing) does not satisfy below-20 ℃.

Its Heating temperature of experiment No.54 is 900 ℃, and accumulating draft in addition is 100%, and the discontented foot-eye value of the yield ratio YR after the cold bend(ing) is below 85%.Testing its accumulation draft of No.55 in addition is 80%, and the discontented foot-eye value of the yield ratio YR after the cold bend(ing) is below 85%.

Its acceleration cooling beginning temperature after rolling of experiment No.58 is 760 ℃, and polygonal ferrite branch rate is 80 area %, and tensile strength TS reduces.

It is 580 ℃ that its acceleration cooling after rolling of experiment No.60 stops temperature, because bainite reduces and perlite generates when quickening cooling, so tensile strength TS reduces.

Its acceleration speed of cooling after rolling of experiment No.61 is 1.5 ℃/second, because bainite reduces and perlite generates when quickening cooling, so tensile strength TS reduces.

Its preceding reheat temperature of quenching of experiment No.63 is 850 ℃, and polygonal ferrite branch rate is 35 area %, and the discontented foot-eye value of the yield ratio YR after the cold bend(ing) is below 85%.

Its reheat temperature before quenching of experiment No.66 is to be right after 700 ℃ of Ac1, because the perlite that generates when reheat before quenching is heated up is remaining, so tensile strength TS reduces.

Its tempering temperature of experiment No.68 is 600 ℃, and polygonal ferrite branch rate is 80 area %, and tensile strength TS reduces, and the discontented foot-eye value of the yield ratio YR after the cold bend(ing) is below 85%.

T/d during its cold shaping of experiment No.70 is 15%, and the discontented foot-eye value of the yield ratio YR after the cold bend(ing) is below 85%.

With respect to this, in every (test No.4～13,16,17,19～21,23,25～28,30,31,34,36,37,39～50,52,53,56,57,59,62,64,65,67,69,71) of the important document that satisfies the present invention's regulation, whole characteristics all satisfies target value.

Also have, the main points in the manufacturing of experiment No.4～71 are as follows.That is, experiment No.4～38, the steel that the chemical ingredients shown in the described table 1,2 is formed carry out two-phase territory temperature and quench (Q ') after rolling end, and experiment No.39 has further implemented temper (T).

No.40 is after rolling end in experiment, quickens cooling and stops at 450 ℃, and experiment No.41 has further implemented temper (T).

Experiment No.42 carries out slow cooling (air cooling) after rolling end, carry out direct quenching (DQ ') from two phase region temperature, and experiment No.43 has further implemented temper (T).

No.44 is after rolling end in experiment, is quickening cooling above the Ar1 point to being lower than the Ar3 point, and air cooling kept 60 seconds thereafter, and polygonal ferrite α P is generated, and then carried out direct quenching.

No.45 is after rolling end in experiment, quickening cooling to being lower than the Ar3 point above the Ar1 point, remain on two phase region temperature with online maintenance stove thereafter, polygonal ferrite α P is generated, then quench, experiment No.46 has further implemented temper (T).

Experiment No.47,48 makes t/d be changed to 7.5,5 (%) in the scope of the present invention's regulation.Experiment No.49 is that thickness of slab is the result of 40mm.Experiment No.50 bends after 400 ℃ of intensifications.

Experiment No.51～54 make Heating temperature 900～1300 ℃ range with specified chemical composition of the present invention.Experiment No.55～58 with specified chemical composition of the present invention, make the acceleration cooling beginning temperature variation after rolling.

Experiment No.59,60 with specified chemical composition of the present invention, makes to quicken to cool off to stop temperature variation.Experiment No.60～62 with specified chemical composition of the present invention, change the acceleration speed of cooling after rolling.

Experiment No.63～66, with specified chemical composition of the present invention, the Heating temperature when making quenching (Q ') change.Experiment No.67,68 with specified chemical composition of the present invention, changes tempering temperature (T).

Experiment No.69 with specified chemical composition of the present invention, carries out online levelling machine and corrects before quickening cooling.Experiment No.70 with specified chemical composition of the present invention, makes the cold t/d of song that becomes outside the scope of the present invention's regulation.The experiment No.71, with specified chemical composition of the present invention, with the bending forming temperature as 400 ℃.

[table 6]

Test No.	Steel plate				t/d (％)	The steel pipe pipe									Y type welding crack test crackle prevent preheating temperature (℃)	HAZ toughness
																		t/4，L，JIS4			The kind of microtexture	Ferritic phase		Island martensite body phase		Surplus (area %)	t/4，L，JIS4				Heat input (kJ/mm)	vE0 (J)
	YP (MPa)	TS (MPa)	δu (％)	α p (area %)		α q (area %)	Ratio (area %)	Aspect ratio	YP (MPa)	TS (MPa)	YR (％)	vTrs (℃)
													1	360		500	25	αp+P	10	70		0	0	-	30(P)		420	520	80.8	-10			50	10	40
2	390	510	21	αq+B	10	0	30	0	-	70(B)	470	530			88.7						-40					25					10	150
													3	370		495	22	αp+αq+B	10	30		30	0	-	40(B)		445	515	86.4	-55			25	10	150
4	375	525	20	αp+αq+B+(M-A)	10	60	10	2	2.1	28(B)	445	545			81.7						-50					25					10	170
													5	370		525	21	αp+αq+B+(M-A)	10	55		10	2	2.0	28(B)		440	545	80.7	-45			25	10	150
6	365	540	21	αp+αq+B+(M-A)	10	65	5	2	2.0	28(B)	435	560			77.7						-60					25					10	180
													7	350		545	18	αp+αq+B+(M-A)	10	50		5	2	1.8	40(B)		425	565	75.2	-45			25	10	150
8	365	530	25	αp+αq+B+(M-A)	10	40	5	5	4.0	50(B)	465	550			84.5						-70					25					10	200
													9	385		550	25	αp+αq+B+(M-A)	10	50		5	4	3.9	45(B)		470	580	81.0	-75			25	10	210
10	380	500	23	αp+αq+B+(M-A)	10	40	20	5	2.0	35(B)	440	520			84.6						-50					25					10	170
													11	350		495	24	αp+αq+B+(M-A)	10	70		10	1	2.3	19(B)		400	515	77.6	-80			25	10	60
12	355	500	21	αp+αq+B+(M-A)	10	65	15	1	2.0	19(B)	405	520			77.9						-40					25					10	25
													13	380		500	25	αp+αq+B+(M-A)	10	50		5	4	3.8	41(B)		440	520	84.6	-80			25	10	200
14	375	525	18	αp+αq+B	10	60	10	0	-	30(B)	425	540			78.7						-10					25					10	45
													15	390		505	24	αp+αq+B+(M-A)	10	30		30	8	10.0	35(B)		480	525	91.4	-80			25	10	250
16	395	545	24	αp+αq+B+(M-A)	10	40	20	5	4.0	35(B)	475	575			82.6						-80					25					10	220
													17	385		555	20	αp+αq+B	10	60		15	0	-	25(B)		455	575	79.1	-40			25	10	80
18	375	525	20	αp+αq+B	10	60	10	0	-	30(B)	445	545			81.7						-30					25					10	70
													19	275		385	30	αp+αq	10	80		18	0	-	0		335	405	82.7	-100			25	10	250
20	375	525	21	αp+αq+B	10	60	10	0	-	30(B)	445	545			81.7						-35					25					10	130
													21	365		515	22	αp+αq+B	10	65		10	0	-	25(B)		435	535	81.3	-55			25	10	170
22	395	555	22	αp+αq+B	10	10	20	0	-	50(B)	495	575			86.0						-15					25					10	80
													23	360		525	18	αp+αq+B+(M-A)	10	60		20	5	4.0	15(B)		425	535	79.4	-70			25	10	70
24	425	560	17	αp+αq+B+(M-A)	10	40	30	5	4.0	25(B)	475	580			81.8						-40					25					50	45
													25	375		500	25	αp+αq+B+(M-A)	10	55		15	2	2.4	28(B)		425	520	81.7	-80			25	50	250

[table 7]

Test No.	Steel plate				t/d (％)	Steel pipe									Y type welding crack test crackle prevent preheating temperature (℃)	HAZ toughness
																		t/4.L.JIS4			The microtexture kind	Ferritic phase		Island martensite body phase		Surplus (area %)	t/4，L，JIS4				Heat input (kJ/mm)	vE0 (J)
	YP (MFa)	TS (MPa)	δu (％)	α p (area %)		α q (area %)	Ratio (area %)	Aspect ratio	YP (Mpa)	TS (MPa)	YR (％)	vTrs (℃)
													26	410		555	20	αp+αq+B+(M-A)	10	55		15	2	3.0	33(B)		465	575	80.8	-40			25	10	150
27	345	500	25	αp+αq+B+(M-A)	10	65	15	4	3.0	18(B)	410	525			78.1						-70					25					10	280
													28	448		560	30	αp+αq+B+(M-A)	10	40		25	5	4.0	20(B)		490	500	84.4	-20			50	10	50
29	455	570	30	αp+αq+B+(M-A)	10	20	30	8	4.0	42(B)	510	580			87.9						-10					50					10	27
													30	390		535	22	αp+αq+B+(M-A)	10	55		20	1	3.1	24(B)		450	550	81.8	-50			25	10	230
31	440	550	26	αp+αq+B+(M-A)	10	40	10	5	4.0	45(B)	480	570			84.2						-90					25					10	180
													32	400		530	23	αp+αq+B+(M-A)	10	45		15	4	3.8	36(B)		455	540	84.2	-25			50	10	80
33	425	560	26	αp+αq+B+(M-A)	10	35	20	8	3.0	42(B)	490	570			86.0						-90					50					10	190
													34	390		525	20	αp+αq+B+(M-A)	10	50		10	5	3.5	35(B)		460	550	83.6	-50			50	10	100
35	410	535	14	αp+αq+B+(M-A)	10	30	10	8	4.0	55(B)	475	555			86.3						-30					50					10	70
													36	375		525	22	αp+αq+B+(M-A)	10	60		10	2	2.2	28(B)		445	545	81.6	-60			50	10	185
37	375	525	22	αp+αq+B+(M-A)	10	60	10	2	2.0	28(B)	440	545			80.7						-55					50					10	180
													38	375		525	17	αp+αq+B+(M-A)	10	60		10	2	2.2	28(B)		440	545	80.7	-15			50	10	90
39	375	515	27	αp+αq+B	10	60	10	0	2.0	28(B)	425	515			82.5						-65					50					10	170
													40	385		520	25	αp+αq+B+(M-A)	10	60		10	1	2.1	29(B)		430	535	85.0	-60			50	10	170
41	365	505	28	αp+αq+B	10	60	10	0	-	31(B)	430	510			84.4						-70					50					10	170
													42	385		535	25	αp+αq+B+(M-A)	10	50		10	2	2.0	38(B)		465	555	83.7	-35			50	10	170
43	355	505	25	αp+αq+B	10	70	10	0	-	20(B)	430	520			82.6						-45					50					10	170
													44	345		500	25	αp+αq+B+(M-A)	10	65		10	3	2.3	22(B)		420	515	81.5	-20			50	10	170
45	385	535	25	αp+αq+B+(M-A)	10	70	10	5	2.0	15(B)	455	555			82.0						-25					50					10	170
													46	355		510	28	αp+αq+B	10	70		10	0	-	20(b)		425	530	80.1	-40			50	10	170
47	375	525	20	αp+αq+B+(M-A)	7.5	60	10	2	2.1	28(B)	425	540			78.7						-50					50					10	170
													48	375		525	20	αp+αq+B+(M-A)	5	60		10	2	2.0	28(B)		415	535	77.6	-55			50	10	170
49	410	565	20	αp+αq+B+(M-A)	10	55	15	1	1.8	28(B)	465	585			79.4						-65					50					10	200
													50	370		520	21	αp+αq+B	10(400℃)	60		10	0	-	30(B)		440	540	81.5	-50			50	10	170

[table 8]

Test No.	Steel plate				t/d (％)	Steel pipe									Y type welding crack test crackle prevent preheating temperature (℃)	HAZ toughness
																		t/4，L，JIS4			The kind of microtexture	Ferritic phase		Island martensite body phase		Surplus (area %)	t/4，L，JIS4				Hot input (kJ/mm)	vE0 (J)
	YP (MPa)	TS (MPa)	δu (％)	α p (area %)		α q (area %)	Ratio (area %)	Aspect ratio	YP (MPa)	TS (MPa)	YR (％)	vTrs (℃)
													51	375		530	18	αp+αq+B+(M-A)	10	60		10	2	3.0	25(B)		450	555	81.8	-15			25	10	170
52	370	528	19	αp+αq+B+(M-A)	10	60	10	2	2.0	26(B)	445	550			80.9						-30					25					10	170
													53	385		515	22	αp+αq+B+(M-A)	10	70		10	2	2.0	16(B)		450	540	83.3	-60			25	10	170
54	400	500	24	αp+αq+B+(M-A)	10	75	7	2	2.0	14(B)	475	520			91.3						-65					25					10	170
													55	390		510	23	αp+αq+B+(M-A)	10	72		9	2	2.0	15(B)		455	530	85.8	-60			25	10	170
56	370	540	17	αp+αq+B+(M-A)	10	50	10	2	4.0	34(B)	450	560			80.4						-30					25					10	170
													57	365		510	20	αp+αq+B+(M-A)	10	65		10	2	2.0	21(B)		435	530	82.1	-60			25	10	170
58	325	460	24	αp+αq+B+(M-A)	10	80	5	2	7.0	6(B)	395	480			82.3						-70					25					10	170
													59	345		505	22	αp+αq+B+(M-A)	10	60		10	0.5	2.0	36.5(B)		415	525	79.0	-65			25	10	170
60	300	460	24	αp+αq+B+P+(M-A)	10	64	7	0.2	2.0	15.8(B)，10(P)	385	485			80.2						-70					25					10	170
													61	280		445	25	αp+αq+B+P+(M-A)	10	80		2	1	2.0	5(B)，10(P)		350	465	75.2	-45			25	10	170
62	420	565	20	αp+αq+B+(M-A)	10	50	10	1.5	2.0	36.5(B)	490	585			83.8						-80					25					10	170
													63	420		555	20	αp+αq+B+(M-A)	10	35		20	2	2.0	41(B)		485	565	85.8	-70			25	10	170
64	405	545	20	αp+αq+B+(M-A)	10	40	15	2	2.0	41(B)	475	565			84.0						-40					25					10	170
													65	385		525	22	αp+αq+B+(M-A)	10	65		15	2	2.0	16(B)		455	545	83.5	-65			25	10	170
66	300	460	24	αp+αq+P+B	10	65	5	0	0	10(B)，20(P)	380	480			79.1						-30					25					10	170
													67	375		500	21	αp+αq+B	10	70		7	0	0	23(B)		440	520	85.0	-50			25	10	170
68	335	450	24	αp+αq+B+P	10	80	5	0	0	5(B)，10(P)	405	470			86.2						-70					25					10	170
													69	365		510	20	αp+αq+B+(M-A)	10	60		10	2	2.0	26(B)		435	530	82.1	-45			25	10	170
70	375	525	20	αp+αq+B+(M-A)	15	60	10	2	2.0	26(B)	495	555			89.2						-30					25					10	170
													71	375		525	20	αp+αq+B	10 (400 ℃)	60		10	2	2.0	28(B)		445	545	81.7	-50			25	10	170

Claims (11)

1. a cold shaping steel pipe is characterized in that, in quality %, contains:

C：0.07～0.18％、

Si：0.05～1.0％、

Mn：0.7～1.7％、

Ti：0.002～0.025％、

Sol.Al:0.005～0.1% and

N:0.001～0.008%, and Fe and unavoidable impurities,

Also contain at least a kind that from the group who constitutes by following element, selects:

Below the Cr:0.6%, and contain 0%;

Below the Mo:0.5%, and contain 0%; With

Below the V:0.08%, and contain 0%, wherein,

The ratio of Mn content [Mn] and C content [C] satisfies [Mn]/[C]≤15,

By the carbon equivalent Ceq value shown in following (1) formula in 0.34～0.42% scope,

By the A value shown in following (2) formula in 1.1～2.6 scope,

Microtexture respectively is made of mutually following: the polygonal ferrite phase of 40～70 area %; The quasi-polygonal ferrite phase of 0～20 area %; With the aspect ratio of 0～5 area % be major diameter/minor axis be below 4.0 the island martensite body mutually; Surplus is the bainite phase,

This cold shaping steel pipe is that the steel plate of t obtains from thickness of slab, and having t/d during for d at the outside of described steel pipe cold bend(ing) diameter is cold shaping position below 10%, and wherein, the unit of t, d is mm,

Ceq＝[C]+[Si]/24+[Mn]/6+[Cr]/5+[Mo]/4+[V]/15 …(1)

Wherein, [C], [Si], [Mn], [Cr], [Mo] and [V] represent the content in quality % of C, Si, Mn, Ni, Cr, Mo and V respectively,

A＝(2.16{Cr}+1)×(3.0{Mo}+1)×(1.75{V}+1)…(2)

Wherein, { Cr}, { Mo} and [V} represents Cr, Mo and the V solid solution capacity in quality % in steel plate respectively.

2. cold shaping steel pipe according to claim 1 is characterized in that, in quality %, also contains below Cu:0.5% but does not contain 0% and below the Ni:3.0% but do not contain select 0% at least a.

3. cold shaping steel pipe according to claim 1 is characterized in that, in quality %, also contains below the Nb:0.015%, but does not contain 0%.

4. cold shaping steel pipe according to claim 1 is characterized in that, in quality %, also contains below the Ca:0.005%, but does not contain 0%.

5. cold shaping steel pipe according to claim 1 is characterized in that, in quality %, also contains rare earth element: below 0.02% but do not contain 0%.

6. a method of making claim 1,2,4,5 described cold shaping steel pipes is characterized in that, comprises following operation:

Steel billet is heated to 950～1250 ℃ temperature range;

Rolling described steel billet is made steel plate, and the accumulation draft when making the austenite non-recrystallization temperature A γ that is in shown in following (3) formula following becomes below 60%, comprising 0%;

With 4～100 ℃/second speed of cooling described steel plate is quickened to be cooled to below 450 ℃ from the temperature more than the Ar3 transformation temperature;

Will speed up the temperature range of cooled described steel plate reheat to 730～830 ℃, then quench;

Is that scope below 10% is carried out cold shaping with the described steel plate after quenching at described t/d,

Aγ＝887+467[C]+(732[V]-230[V])+890[Ti]+363[Al]-357[Si] …(3)

Wherein, [C], [V], [Ti], [Al] and [Si] represent that respectively the content in quality % of C, V, Ti, sol.Al and Si, the unit of A γ are ℃.

7. the manufacture method of cold shaping steel pipe according to claim 6 is characterized in that, the temperature range of reheat to 730～830 ℃ was then carried out the described steel plate that quenches, is implementing tempering below 500 ℃.

8. the manufacture method of cold shaping steel pipe according to claim 6 is characterized in that, for the described described steel plate after rolling that is through with, carried out online levelling machine and correct before described acceleration cooling.

9. the manufacture method of cold shaping steel pipe according to claim 6 is characterized in that, steel billet temperature is made as below 400 ℃ and carries out described cold shaping.

10. cold shaping steel pipe according to claim 2 is characterized in that,

By following formula (1) ' shown in carbon equivalent ceq ' value in 0.34～0.42% scope,

Ceq’＝[C]+[Si]/24+[Mn]/6+[Ni]/40+[Cr]/5+[Mo]/4+[V]/15 …(1)’

Wherein, [C], [Si], [Mn], [Ni], [Cr], [Mo] and [V] represent the content in quality % of C, Si, Mn, Ni, Cr, Mo and V respectively.

11. a method of making the described cold shaping steel pipe of claim 3 is characterized in that, comprises following operation:

Steel billet is heated to 950～1250 ℃ temperature range;

Rolling described steel billet is made steel plate, makes to be in following (3) ' accumulation draft when the austenite non-recrystallization temperature A γ ' shown in the formula is following becomes below 60%, comprising 0%;

With 4～100 ℃/second speed of cooling described steel plate is quickened to be cooled to below 450 ℃ from the temperature more than the Ar3 transformation temperature;

Will speed up the temperature range of cooled described steel plate reheat to 730～830 ℃, then quench;

Is that scope below 10% is carried out cold shaping with the described steel plate after quenching at described t/d,

Aγ’＝887+467[C]+(6445[Nb]-644[Nb])+(732[V]-230[V])+890[Ti]+363[Al]-357[Si] …(3)’

Wherein, [C], [Nb], [V], [Ti], [Al] and [Si] represent that respectively the content in quality % of C, Nb, V, Ti, sol.Al and Si, the unit of A γ ' are ℃.